The present disclosure relates to a solid form of 6-carboxy-2-(3, 5-dichlorophenyl)-benzoxazole meglumine salt, also named as Tafamidis meglumine, which is used for treating transthyretin amyloidosis in mammal. Tafamidis meglumine stabilizes the protein transthyretin (TTR), dissociation of which is implicated in TTR amyloidosis and is being developed for the treatment of transthyretin familial amyloid polyneuropathy. Tafamidis meglumine is developed by Pfizer and is marketed in the European Union as Vyndaqel since 2011. The structure is shown as formula (I):

Polymorph or polymorphism is the property of some molecules or molecular complexes. Polymorphism may result from different molecular packing. Polymorphs of a given compound may have different crystal structures and physical properties, such as solubility, stability, thermal property, mechanical property, purification ability, X-ray powder diffraction, infrared spectroscopy, Raman spectroscopy, and solid-state NMR spectroscopy, etc. One or combination of multiple characterization methods may be used to differentiate different crystalline forms of the same molecule or molecular complexes. Novel crystalline forms (including anhydrates, hydrates and solvates) of the active pharmaceutical ingredients may offer better processing and physicochemical properties, such as bioavailability, stability, processability, and purification ability. Some novel crystalline forms may serve as intermediate crystal forms to facilitate solid state transformation to desired forms. Novel polymorphs of raw materials provide more solid forms in the formulation, and this can improve dissolution, improve shelf life, and make it easier to process.
CN100448852C firstly disclosed the preparation and salts of Tafamidis. CN103781770B disclosed crystalline form M, liquid crystalline form B and amorphous form A of Tafamidis meglumine (which is incorporated herein by reference). The amorphous form A has poor stability and would convert to liquid crystalline form B spontaneously when stored for some time. Liquid crystalline form B is highly deliquescent and the weight gain is up to 25% when stored at 90% relative humidity, thus form B is not suitable for drug development. By now, crystalline form M is the only form which can be used for drug development, and is also used for scaled up production of active pharmaceutical ingredients (API). The X-ray powder diffraction pattern of crystalline form M shows diffraction peaks at 2 theta values of 10.7°±0.2°, 11.8°±0.2°, 13.3°±0.2°, 14.8°±0.2° and 21.7°±0.2°. In addition to the above-described polymorphs, no other crystalline form is disclosed. Studies show that hygroscopicity of crystalline form M is high, thus resulting in high cost in storage. Therefore, it is still significant to develop a novel crystalline form with lower hygroscopicity that can be used for drug development. With lots of experiments being carried out, inventors of the present application finally find novel crystalline form E of Tafamidis meglumine which is beneficial for production and development process. The crystalline form E has advantages of good stability, simple preparation process, low hygroscopicity and good purification effect. It is also beneficial to drug's long-term storage. Crystalline form E provides a new and better choice for the development of Tafamidis meglumine drug product.